1. Technical Field
This disclosure relates generally to an ignition coil for use in producing an electric spark in a spark plug for use in internal combustion engines.
2. Background Art
Typical ignition coils for use in internal combustion engines are equipped with a primary coil and a secondary coil. The primary coil is made up of a primary spool and a primary winding wound around the primary spool. Similarly, the secondary coil is made up of a secondary spool and a secondary winding wound around the secondary spool. The primary coil and the secondary coil are disposed coaxially as a coil assembly within a casing. The coil assembly is fit at an end thereof in a hole of a connector casing in which an igniter is installed.
After the primary winding is wound around the outer periphery of the primary spool, ends of the primary winding are coupled to terminals mounted on the primary spool The terminals of the primary spool are resistance-welded to terminals of the connector casing.
Japanese Patent First Publication No. 2003-124043 discloses an ignition coil which has a primary coil. The primary coil includes a primary winding wound around a primary spool. The primary winding has leading and trailing ends retained by winding holders provided in flanges of the primary spool. The retaining of the leading and trailing ends of the primary winding in the winding holders is achieved by fitting terminals on the winding holders. The terminals are disposed directly on a connector, thereby eliminating the need for intermediate terminals in the primary spool.
The ignition coil of the above publication, however, has the leading and trailing ends of the primary winding extending outside the end of the primary spool in the lengthwise direction of the primary spool, thus resulting in an increased overall length of the primary coil. The misalignment of the leading and trailing ends of the primary winding from the terminals when the terminals are put on the winding holders may result in a failure in making contacts between the terminals and the winding holders, which leads to an excess of load on the terminals and deformation thereof. This may result in bad electric connections between the terminals and the primary winding.
The primary winding is coated with an electric insulation. The structure of the above publication may result in a failure in stripping the electric insulation from the primary winding when the terminals are put on the leading and trailing ends of the primary winding.